Published European Patent Application 849 597 describes a tire comprising at least one magnetized area which can be used for instance for providing information about the rotary speed of the tire when mounted on a vehicle and to measure other physical quantities. The subject of this published patent application is a tire that, at least at one predetermined location, contains a rubber mixture that is permeated with magnetizable particles. These magnetizable locations, in general an annular band in the sidewall of the tire, have successive sections of alternating magnetization, either equidistant or in a pattern. Thus, with the aid of a sensor that is secured to the chassis, not only the rotational speed of the respective wheel can be provided, but also, by measuring the tire distortion through deflection of the applied magnetized sections, forces acting on the tires can be determined.
This known tire is manufactured by mixing ferromagnetic particles into the rubber mixture which is applied to the area where the magnetization is carried out. The magnetization is then achieved by applying magnetic fields with lines of flux that extend in the peripheral direction of the tire in alternating polarizations. This magnetization is effected after installation of the magnetizable rubber mixture and after vulcanization thereof. Also described is an apparatus to carry out the magnetization.
It has been found, however, that, on the tire described, the desired magnetization is very hard to achieve. Depending on the method applied, either there is no identifiable signal at all, or the magnetized areas of opposite polarizations are not separated by the desired narrow line but, instead, wide lines are formed which blur and distort the signals detected by a respective sensor. Thus the measurements obtained are imprecise.